This invention is related to displacement apparatus for distributing high temperature gases and atmospheres in high-temperature environments and, more specifically, to high-temperature-resistant fan apparatus.
High temperature furnaces and ovens are commonly employed in industry for use in heat treating metal parts and products. Such furnaces are commercially available from sources such as Ipsen, Inc. of Rockford, Ill., Oven Systems, Inc. of Milwaukee, Wis. and Flinn and Dreffein Engineering Co. of Northbrook, Ill. These high-temperature furnaces typically consist of a rectangular furnace body having a top wall, side walls and a bottom wall. The furnace walls define a furnace interior or chamber in which the parts or other articles to be heated are placed. The furnace walls typically have a thickness (i.e., a dimension between the wall outer and inner surfaces) on the order of about 8 to 10 inches. One or more doors are provided in the furnace walls for purposes of moving the parts and products into and out of the furnace interior.
The furnace interior is typically heated by use of gas-fired burners positioned along the furnace top and/or bottom walls. Heated air or other gas is directed from the burners into one or more heating elements positioned through the furnace top and/or bottom walls and within the furnace interior. Heat transfer from the elements to the furnace interior heats the furnace interior to the desired temperature, typically (but not exclusively) in the range of about 1000 to 1850xc2x0 F. Gas burners for use in heating high temperature furnaces may include, for example, single ended recuperative burners available from Eclipse Combustion, Inc. of Rockford, Ill.
Heat treating of metal parts and products within the furnace is an exacting and demanding process. In order to uniformly heat treat parts within the furnace the operator must carefully control conditions within the furnace. To this end, it is essential that a uniform temperature be maintained within the furnace and that thermal gradients be avoided. Gases such as nitrogen and hydrogen are frequently introduced into the furnace interior in order to impart particular properties to the parts and metal products. Such gases, and the atmosphere generally, must be uniformly distributed within the furnace interior. The furnace and its components must be designed to withstand the elevated furnace temperatures as well as the corrosive environment created by the gases and materials within the furnace.
Fans, such as xe2x80x9cplug fans,xe2x80x9d have been developed in an effort to provide a uniform temperature within the furnace and to evenly distribute the furnace atmosphere. A plug fan typically consists of a frame which is inserted, or plugged, into an opening in the furnace top wall. Fan blades mounted on a fan shaft extend from the frame into the furnace interior. The fan shaft is rotatably mounted on one or more bearings located within the frame or outside of the furnace. A motor coupled to the fan shaft rotates the shaft so as to rotate the fan blades within the furnace interior. Rotation of the fan blades within the furnace interior displaces the furnace atmosphere and uniformly distributes the temperature and gases within the furnace interior. Commercial sources of plug fans include Alloy Engineering Co. of Berea, Ohio and Industrial Gas Engineering Co., Inc. of Westmont, Ill.
A major shortcoming of prior art plug fans used in connection with high temperature furnaces is that the harsh operating environment and high temperatures of such furnaces rapidly damage the fan thereby shortening the fan""s useful life. Thermodynamic heat transfer in the form of conduction, radiation and convection all act to damage the fan. For example, heat from within the furnace interior is conducted through the fan and fan shaft into the bearings supporting the fan shaft. Radiant and convection heat can be transferred along the fan shaft or through the fan frame to the bearings, fan motor and other fan components. Such heat transfer causes the bearings and other fan components to fail requiring replacement or extensive repair of the fan. Standard bearings are particularly susceptible to failure at temperatures of approximately 300xc2x0 F. at which point typical lubricants fail resulting in bearing failure and damage to the fan. Direct costs are incurred to replace or repair the fan and indirect costs are incurred based on the operator""s inability to operate the furnace.
In an effort to limit heat and furnace-related fan damage and extend the useful life of the fan, certain fans have been equipped with separate, active cooling systems. Such active cooling systems are provided to remove heat from the fan shaft and fan frame thereby limiting heat transfer into, and failure of, the bearings and other components. For example, certain plug fans are provided with a water-cooled frame. Chilled water is piped under pressure through the frame in order to remove heat from the fan. Other plug fans utilize compressed air cooling systems in which heat is removed from the fan by passing a stream of compressed air over the fan.
Such active cooling apparatus disadvantageously adds unnecessary cost to the fan both in terms of the cooling apparatus and in terms of the cost to operate such apparatus. The cooling apparatus may be subject to failure, for example, if impurities within the coolant supply line limit the flow of coolant to the bearings. And, inclusion of such active cooling apparatus with the fan adds a further maintenance item with respect to operation of the furnace.
Other applications may have high-temperature environments which require apparatus to displace gases within said environments. The foregoing problems with respect to the fan apparatus used in furnaces can also affect these other applications. The apparatus selected for use in displacing high temperature gases must be resistant to damage from the elevated temperatures yet at the same time be durable and economical to operate.
An improved fan for use in high-temperature environments, such as those found in heat treating furnaces, which would facilitate displacement of the atmosphere within such environments resulting in uniform temperatures and gas distribution yet would not require any separate active cooling apparatus would represent an important advance in the art.
It is an object of this invention to provide improved high-temperature fan apparatus overcoming some of the problems and shortcomings of the prior art.
An important object of this invention is to provide improved high-temperature fan apparatus which are high-temperature resistant.
It is also an object of the invention to provide improved high-temperature fan apparatus capable of operation in high-temperature environments without separate active fan-cooling apparatus.
A further object of the invention is to provide improved high-temperature fan apparatus which limit heat transfer through the fan thereby extending the useful life of the fan.
Yet another object of the invention is to provide improved high-temperature fan apparatus which are resistant to corrosive conditions found in high-temperature environments.
Another object is to provide improved high-temperature fan apparatus which are economical to manufacture and maintain.
Still another object of the invention is to provide improved high-temperature fan apparatus which may be easily adapted for use in many different high-temperature applications.
How these and other objects are accomplished will be apparent from the following descriptions and from the drawings.
Briefly described, the invention is fan apparatus for circulating high temperature gas comprising the atmosphere within a chamber, most typically the chamber comprising a furnace interior. The invention is described herein with respect to an exemplary furnace but could be used in other high temperature applications. The high-temperature fan apparatus is specially designed to limit heat transfer through the fan apparatus, particularly to the bearings and other heat-sensitive components. The novel fan structure advantageously extends the useful life of the fan and yet avoids any need for separate, active fan-cooling apparatus.
In general, preferred forms of the fan include a frame, a fan shaft rotatably secured with respect to the frame, a fan element secured along the shaft and thermal barrier material secured with respect to the frame.
The frame is preferably provided with support surfaces configured to support the fan apparatus. The frame may be configured to support the fan at an opening in a wall, such as the wall of a furnace. Alternatively, the frame may be configured to support the fan with respect to other structure closely associated with the furnace. A highly preferred form of the frame is configured to be positioned at least partially in the wall opening and the frame and thermal barrier material are conformably shaped to said opening. It is most highly preferred that the frame includes a substantially flat back plate and at least one sidewall secured to and projecting outwardly from the back plate. Preferably, the at least one sidewall and back plate form a cavity in which the thermal barrier material is secured.
The fan shaft is supported for rotation, preferably by at least one bearing member at a position outside the chamber or interior of the furnace. The fan shaft has first and second ends and a shaft outer surface therebetween. In highly preferred embodiments, the shaft is sized to support the fan element through the wall opening and within the chamber. It is highly preferred that the shaft include at least one bore positioned trans-axially through at least a portion of the shaft at a position between the chamber and the at least one bearing member. The at least one bore is provided to limit heat transfer across the bore and toward the shaft second end. It is highly preferred that the such bore structure extends entirely through the shaft. Most preferably, the shaft includes first and second co-planar bores and each bore is positioned along an axis transverse to the other and normal to the shaft.
Preferred forms of the high-temperature fan apparatus further include a bearing mount secured with respect to the frame. First and second axially-aligned bearings are secured to the bearing mount. The fan shaft of this embodiment is journaled in the bearings.
It is preferred that at least the first bearing include structure designed to limit heat transfer from the fan shaft to the bearing. The preferred bearing structure preferably comprises an inner race, an outer race and ball bearings positioned therebetween. The inner race has an inner surface facing the fan shaft and an inside diameter. A pin projects radially inwardly from the inner race. The fan shaft of this embodiment includes an opening keyed to the pin for co-rotation of the shaft and inner race. In addition, the shaft is sized so that the shaft has a diameter which is less than the inner race inside diameter. As a result of this structure, the shaft outside surface and inner race inner surface contact along less than all of the respective surfaces when the shaft is journaled in the first bearing. Such structure limits heat transfer into the first bearing.
The most highly preferred high-temperature fan apparatus includes a fan element which includes plural fan blades secured at one end along the fan shaft and extending radially outwardly from said shaft. Other types of fan elements may be used with the invention.
The thermal barrier material includes an opening through which the shaft is rotatably positioned. Thermal barrier material with shaft-contact surfaces is provided along the opening in direct contact with the shaft to limit heat transfer through the frame and along the shaft outer surface. Preferably, the thermal barrier material comprises, at least in part, plural insulation elements. Each element has side walls, end walls, an inner edge surface positioned to face the furnace interior and an opposed outer edge surface. The preferred elements are arranged one after the other so that adjacent sidewalls abut. It is highly preferred that the thermal barrier material further includes heat-resistant barrier material applied along the insulation element inner edge surfaces.
The shaft may be rotated by a motor coupled in torque-transmitting relationship to the shaft. The motor is preferably coupled to the shaft at a position between the bore and shaft second end. The motor is preferably secured with respect to the frame at a motor mount. The motor is coupled to the shaft by horsepower-transmitting members. Preferably, the horsepower-transmitting members are a first pulley secured for co-rotation with a motor shaft, a second pulley secured for co-rotation with the fan shaft and a belt linking the pulleys.